If "no one" means exactly zero person beside yourself you would be right. To grow from exactly zero to a few dozens of potential customers you don't need marketing. You need to tell people what you built. This is not an euphemism for marketing, its exactly what it means, to tell people that you build it. The very first sale must come from yourself telling people you already know pra reaching people in online forums. I don't classify this as "marketing".

At most, you need to do sales, not marketing.